optionMONSTER's Depth Charge monitoring system detected the purchase of about 3,000 August 45 puts for $0.55 and the sale of an equal number of August 55 calls for $0.55. Volume was more than 9 times open interest at both strikes, indicating that new positions were initiated.

The investor probably owns shares in the real estate-brokerage stock and is using the options as a hedge. He or she now has a minimum selling price of $45 and a maximum of $55 through expiration. It cost nothing to implement the strategy, which is known as a collar because it limits the amount of money that can be made to the upside or lost to the downside. (See our Education section)

RLGY rose 1.42 percent to $49.99 yesterday and is almost exactly in the middle of its range over the last three months. Housing numbers--including starts and building permits released yesterday morning--have shown signs of slowing recently, which could make some investors nervous about the stock heading into quarterly results on July 24.

optionMONSTER® provides stock market insight, advanced options education, and actionable trade ideas to meet the needs of do-it-yourself investors. After spending decades in the trading pits of Chicago, Jon 'DRJ' and Pete Najarian founded the company in 2005 to help people better manage their own investment portfolios.